1. Field of the Invention
The present invention relates to a gateway device, a communication method and a program.
2. Description of the Related Art
A system of a so-called Internet Protocol Television (IPTV) service delivering video content using Internet Protocol (IP) is being developed and commercialized by various vendors such as Microsoft Corporation, US. In recent years, an IPTV service using an IP Multimedia Subsystem (IMS) is attracting attention.
The IMS is basically a communication scheme developed by 3rd Generation Partnership Project (3GPP) as an infrastructure technology providing, aside from telephone service for voice, additional services of multimedia in a wireless communication infrastructure of a mobile telephone. The IMS is built based on IP technology, and has high affinity with the infrastructure of the fixed-line Internet. Further, in the trend of integrating by IP wired/wireless communication network infrastructures, i.e. so-called Fixed Mobile Convergence (FMC), by applying the IMS to IPTV, Quality of Service (QoS) for content delivery can be realized, and at the same time, a communication service such as sending of a message to a mobile telephone or chat can be provided in coordination with the IPTV service.
FIG. 1 shows an architecture of the IPTV system using the IMS. As shown in FIG. 1, the IMS is configured by functional elements, such as a Home Subscriber Subsystem (HSS) 24, an Application Server (AS) 26 and the like, with a functional element called a Call Session Control Function (CSCF) 22 based on Session Initiation Protocol (SIP) as the core. The SIP is a communication protocol defined by Request For Comment-3261 (RFC-3261) of Internet Engineering Task Force (IETF).
The mechanism of such IMS is schematically described. User terminals 10 and 12, for which user IDs are set, access the CSCF 22 of an IMS network 20, and registration of the user terminal 10 and 12 and setting control of a session are performed. During this procedure, a process by the AS 26 corresponding to a necessary service is initiated according to the setting of a user profile registered in the HSS 24. The AS 26 is a server for performing a process to actually provide individual service.
For example, with a chat application (PushToTalk) which is an example of a service using the IMS, the user terminal 12 which is, for example, a mobile telephone, connects to the AS 26 in charge of PushToTalk in the IMS network 20 via a mobile telephone network 40. Then, the user terminal 12 establishes a session with the terminals of a plurality of registered group members (not shown) through the AS 26, and by using Voice over Internet Protocol (VoIP), communicates with the members via a relay server.
Further, as another example of the service using the IMS, in the IPTV system of the IMS, the AS 26 of the IPTV service is provided in the IMS network 20. The user terminal 10 at home, for example, a Set Top Box (STB), can receive the IPTV service by being connected to the AS (IPTV) 26 in the same manner. The AS (IPTV) 26 realizes an IPTV service 30 in cooperation with an Electronic Program Guide Server (EPG server) 32 actually managing the IPTV service 30 and a video server 34 delivering video contents.